Paper: batch variations in contrast & sensitivity?
I'm a printing-n00b; only done 15 so far. Have used grades 1, 2 and 2.5, no dodging or burning yet.
What I'd like to know is, how much variation in contrast & sensitivity can I expect between two packs of the same paper type, most likely an Ilford MGIV pearl (44m)? Reason being, I'd like to do test strips and a few whole test prints in varying contrast at 5x7 before laying down a 12x16 or larger.
Can I compute a time ratio based on the area ratio of the enlargements or will I get bitten by sensitivity differences or reciprocity failure in the paper? Assuming I run a test strip to get a new exposure for the larger size, can I assume the contrast will be the same?
In other words, can I get away with 0 or 1 test strips from the larger pack after doing all my experimenting with the smaller pack?
Ilford paper is normally pretty good from batch to batch. What you did not say was if the two paper packets have the same batch number or not? If they do, you should not have any problems. If they are different, there 'should' be no problem either, but the potential for a variance even if ever so slight, is there. I doubt you would see it if each different batch was relatively new. I would not sweat it at this point.
I have done what you suggested for years with reasonable success. There is a variation from batch to batch, but it is small with quality papers like Ilford. You will, however, get some contrast loss with aging paper. You will get more from reciprocity failure, and you will get some from latent image stability or the lack thereof.
To eliminate as many variables as possible, cut your test strips from the box of paper you intend to print on. If you have to, compensate for enlarger height adjustments use the following formula and note to enter the lens-to-paper distance and not the lens-to-negative distance. This will not compensate for reciprocity though!
newTime = oldTime * (newHeight/oldHeight)^2
With Ilford the papers should match within a 1/2 stop and 1/2 a grade or so.
To find out the difference between the boxes make parallel test strips with each paper at 1/10 stop (or 1 second) intervals with no negative in the enlarger - one at the highlights and one at 18% gray midtones. This will tell you if the speeds match and if the contrast range matches.
Recently, I ran through 5 boxes of 12x16 Ilford Multigrade RC within a couple of weeks
All were different emulsion batches
All were the same speed within 1/12 of a stop and the contrast varied only fractionally
I was frankly amazed at how consistent the stuff was box to box.
Ilford Quality Control are certainly on top of their game.
So in theory you can do what you are suggesting and be almost spot-on but I would run a test strip just in case - to cover reciprocity and other possible unknowns
What you cannot do is mix paper surfaces, if you use Gloss in the smaller size and Pearl in the larger, then sadly, it won’t work.
The surface finish affects the overall tonal range a print can achieve and this affects where you choose to place the various print tones
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thanks guys! I'll be getting a couple of fresh packs this week, no idea if they'll be the same batch but they ought to be fairly new.